1. Field of the Invention
The present invention relates to a turbulence avoidance operation assist device by which a pilot is notified of an optimal trajectory for emergency avoidance when a dangerous state such as turbulence is detected in a distant region at a distance of about 20 km ahead of an aircraft in flight. Turbulence represents a typical dangerous state, but the present invention can be also applied in the case of ice crystals or volcano ash.
2. Description of the Related Art
Turbulence has recently attracted attention as a main cause of aircraft accidents, and a Doppler lidar using a laser beam has been researched and developed as an airborne device that detects turbulence in advance (see, for example, Japanese Patent Application Laid-open No. 2003-014845 “Wind Terbulence Prediction System”, Jan. 15, 2003, and H. Inokuchi, H. Tanaka, and T. Ando, “Development of an Onboard Doppler LIDAR for Flight Safety,” Journal of Aircraft, Vol. 46, No. 4, pp. 1411-1415, AIAA, July-August 2009). Lidar is an abbreviation for “Light Detection And Ranging”, that is, a technique for detection that uses light. With this technique, an irradiated light beam is scattered by fine aerosol floating in the atmosphere, the scattered beam is received, and the frequency variation amount (wavelength variation amount) according to the Doppler effect is measured, whereby the wind velocity is measured. Accordingly, the method is called Doppler lidar. Airborne weather radars that have already found practical use have an effective range as large as several hundreds of kilometers. In the usual mode, the observation screen is displayed at all times and the pilot can look at the screen as necessary, thereby making it possible to take the appropriate measures in advance. However, since the weather radars use scattering of microwaves on water droplets contained in the atmosphere, they are not effective when the sky is clear. By contrast, the Doppler lidar is effective when the sky is clear, but the effective range is greatly limited by comparison with that of the weather radars. Therefore, when the pilot determines the degree of danger and starts an optimal avoidance maneuver, while monitoring the display screen, the time interval for taking appropriate measures is short and therefore the probability of human error is high. Therefore, when the optimal avoidance trajectory is automatically determined by a device and a function of notifying the pilot of this trajectory is provided, the pilot may maneuver the aircraft according to this trajectory and the load on the pilot can be reduced.
The effective distance of a Doppler lidar is about 10 km and this short distance impedes the practical use thereof. Accordingly, methods for extending this distance have been researched and developed. However, since the Doppler lidar is an airborne device, strict restrictions are placed on the size, weight, and power consumption thereof and a significant increase in output is difficult to achieve. The improvements over the next several years can extend the distance only to about 20 km. Further significant increase in the distance is also impossible because the lidar uses light waves. A very large number of conditions can be considered for emergency avoidance maneuvers, but if a distance necessary to change a heading azimuth of a passenger jet aircraft by 90 degrees at a maximum cruise velocity of 250 m/s is calculated by way of simple example, the distance will be 12.8 km at a 30-degree bank turn under normal circumstance and 7.4 km at a maximum 60-degree bank turn allowed for the passenger aircraft. Therefore, aircraft capabilities suggest multiple conditions enabling the avoidance of turbulence even within the present effective range of Doppler lidar. However, the allowed time is actually very limited and it is possible that human decision will fail to select the optimal avoidance flight. In addition, it can be supposed that performing an abrupt operation will increase shaking of the fuselage to a degree larger than that caused by the encounter with turbulence.
When an aircraft encounters turbulence and the fuselage shakes, a pilot report is issued. The number of reports about the encounters with moderate turbulences in Japan is about 10,000 per year, and the number of reports about the encounters with severe turbulences is about 200 per year. Among them, about 1 to 2 encounters per year actually resulted in turbulence-induced accidents. In the case of moderate turbulences, it is not necessary to get involved in emergency avoidance, and a normal avoidance maneuver will apparently be sufficient. However, in the case of severe turbulence, the danger of encounter and the danger of emergency avoidance should be evaluated and a safer means should be used. However, it is difficult for a pilot to evaluate these levels of danger instantaneously and the possibility of making a wrong decision cannot be denied.
According to the present navigational standards, when a passenger aircraft deviates from a present flight path, such deviation should be allowed by an air traffic controller. Therefore, in order to use the device in accordance with the present invention effectively, it is apparently necessary to change the standards so that the instructions of an air traffic controller can be overridden as in a TCAS (Traffic alert and Collision Avoidance System) or to take appropriate measures such as electronic automation of air control services. However, the device can still be effectively used under present standards in a partial flight phase such as landing and flight-path angle change at ascending or descending trajectory. Incidentally, the TCAS malfunctioned in many cases at the initial stage of development and has been confirmed for use only for reference at the initial stage of practical implementation, but reliability thereof has been increased through many years of successful operation and the installation thereof on passenger aircraft is now mandatory. At present, this system overrides the instructions of air traffic controllers.